The race to win one of the largest military deals ever awarded will kick off Friday morning, when Department of Defense officials unveil the arcane criteria they will use to purchase a fleet of airborne tankers from either Boeing Co. or Northrop Grumman Corp.

But what was once a sprint has become a marathon slog as the Pentagon attempts for a fourth time to replace its fleet of 415 Eisenhower-era tankers through contracts expected to total more than $100 billion.

The process that started in 2001 to modernize the half-century-old planes that function as aerial gas stations has made its mark for controversy, with an ethics scandal that ended with jail terms for Boeing executives and countless skirmishes on Capitol Hill over jobs, patriotism and free trade.

Defense officials pledged Thursday to run a competition that was fair and transparent as they gave the rival bidders, members of Congress and the press an overview of the draft request for proposal slated to be released Friday. The Air Force hopes to announce the winner by mid-2010.

They also seek to avoid a replay of last year's debacle, when a decision to award the contract to California-based Northrop and the parent of Airbus SAS was reversed amid a firestorm of negative publicity. After Chicago-based Boeing protested the result, the Government Accountability Office found the contracting process had been compromised by "significant errors."

But Boeing has new political momentum entering this round, analysts said. President Barack Obama is viewed as more receptive than his predecessor to the "buy American" case made by Boeing's supporters.

And the defense giant scored a trade victory when the World Trade Organization ruled the jet at the heart of the Northrop proposal had been developed with illegal government subsidies.

While it is impossible to pick a front-runner based on the little that's known of the technical requirements of the request for proposal, or RFP, said aerospace analyst Richard Aboulafia, "In terms of the political winds, it's definitely Boeing."

The contest already was attracting controversy Thursday, even though it hadn't officially begun.

U.S. Rep. John Murtha, D-Pa., the chairman of the House Appropriations Subcommittee on Defense, said he would push to increase the number of tankers built annually to 36 jets rather than the 15 to be proposed by the government.

Doing so would ensure that the latest contest results won't be challenged by the losing team or their congressional supporters, analysts said. It also would speed up the rate at which the aging tankers are grounded, saving billions of dollars in repairs while making it economical for the contractors to split the award.

Murtha's provision is contained in the defense appropriations bill passed by the House, but it is not in the Senate's version. Sources think some of the compromise language likely will wind up in the final version of the bill that House and Senate leaders will begin to hash out next week.

But Defense Secretary Robert Gates opposes splitting the tanker contract, saying it would be too costly to maintain separate depots of spare parts for the two jets and train pilots to fly them. That could lead to another showdown between Congress and Gates, who has vowed to press Obama to veto any defense budget that is laden with unneeded spending.

"I think we're through that debate," Deputy Defense Secretary William Lynn told reporters. "The RFP allows us to make a dual buy, and the RFP allows us to make no award. Our plan is to make a single award."

Meanwhile, to the ire of some Boeing supporters, Lynn and other defense officials indicated Thursday that they wouldn't penalize Northrop and partner Airbus SAS for proposing a tanker based on the Airbus A330, one of several Airbus jets whose startup costs were illegally funded, WTO judges found in an interim report this month.

Defense officials decided not to act on the preliminary WTO ruling, which will be followed by a preliminary decision in a separate case brought against Boeing by Airbus for research grants and other government funds it has received.

"You need to complete that process," Lynn said of the overlapping WTO cases. "That process is going to take several years."

A spokesman for Sen. Patty Murray, D-Wash., said she was concerned by the omission and would continue to press Gates to respond to her earlier queries about whether the WTO ruling would be taken into account during the contest.

Northrop spokesman Randy Belote countered that the WTO finding was irrelevant to the competition: "Boeing's supporters must believe that disqualifying Northrop Grumman's tanker offer on WTO and other issues is the only way to guarantee Boeing a win, which implies they feel Boeing won't have the best tanker for the war-fighter."

But one analyst agrees that Boeing could argue it is at a disadvantage since the initial $35 billion contest for 179 tankers would involve a fixed-price contract, leaving the defense firms to pick up the tab for any development cost overruns.

"Once you commit to a price, you have to live with it," said defense analyst Loren Thompson of the Lexington Institute, a Washington, D.C.-based think tank. "Intrinsically, that's easier for a company that gets government subsidies."